1. Field of Invention
The present disclosure relates to downhole pumping systems submersible in well bore fluids. More specifically, the present disclosure relates to an electrical submersible pump system having a positive displacement pump equipped with a gas escape valve.
2. Description of Prior Art
Submersible pumping systems are often used in hydrocarbon producing wells for pumping fluids from within the wellbore to the surface. These fluids are generally liquids made up of produced liquid hydrocarbon and often water. One type of system used in this application employs an electrical submersible pump (“ESP”) system. ESP systems include a pump operated by an electrically powered motor for pressurizing the fluid. Pressurized fluid is discharged from the pump and into production tubing, or by other means, for conveyance to surface. Often, electrical power may be supplied to the motor via an electrical power cable from the surface that is strapped alongside the tubing. The power cable is sometimes part of an umbilical that extends from the surface; the umbilical can also include control lines for operation of completion equipment disposed in the wellbore below the BSP system. The ESP system is sometimes disposed at the end of a length of tubing deployed in the wellbore, with its discharge coupled to the tubing inlet.
The types of submersible pumps used in wellbores generally include centrifugal pumps, progressive cavity pumps, reciprocating pumps, and positive displacement pumps. Centrifugal and progressive cavity pumps are usually equipped with a rotating impeller or helical rotor to urge the fluid from downhole to the surface. The reciprocating pumps and positive displacement pumps typically operate by reciprocating a sucker rod or piston rod to force wellbore liquid uphole. In any of these designs, vapor lock can occur within the pump when a sufficient amount of gas accompanies the liquid, so that forces applied to the liquid merely compress the gas rather than causing the fluid to be lifted to surface.